I second jimbob's utter tosh and piffle sentiments
The longest I've kept a chicken wrap unrefrigerated is 24 hours. Yes, it's a bit squashed, limp and lifeless but I'm still alive and didn't get gut rot. (wraps fare better in a rucksack than bread and are twice as filling for half the amount)
In these cooler months I wouldn't bat an eyelid at carrying any meaty type sarnie - chances are it's as "chilled" in your rucksack as in a fridge anyway. In summer, I'd be more hesitant (particularly the summer we've just had). In those circumstances I take a non-meaty sarnie - cheese and pickle or egg mayo. If I really needed meat, I'd take a pork pie as they are already preserved/cured so don't need refrigeration.
Ham is a cured meat which is why it has a better unrefrigerated shelf life than chicken. Having said that, all shop bought, pre-cooked and cut meat is processed and salted anyway to increase its shelf life.
If you're still concerned about the "chiller" factor, get one of those squishy insulated packed lunch bags from Asda/Tesco/Aldi/Morrisons/Lidl/Sainsburys/Fortnum & Mason, etc. and pop it in the freezer the night before.